In recent years, precision and speed of a rotary fluid element are more and more increasing due to advancement in technology, and thus higher performance and functionality are required. During operation of a rotary machine, the biggest factors in deterioration of performance of the machine are considered to be vibration and accompanying noise. Thus, to reduce vibration and noise, unbalance of a rotary fluid element should be corrected.
In view of this, a typical method of correcting unbalance of a rotary fluid element has been performed, which is to cut and remove at least one of a part of a nut or a part of a side face of a rotary fluid element in accordance with an amount of unbalance of the rotary fluid element, the nut being provided to mount the rotary fluid element to a rotary shaft.
Further, Patent Document 1 discloses a processing method for correcting unbalance, describing a rotary fluid element (turbine wheel, compressor wheel) of a supercharger as an example of a rotary fluid element. In this processing method for correcting unbalance, a plurality of cut-remove portions is set at a predetermined angular interval in the circumferential direction between blades of a rotary fluid element (turbine wheel, compressor wheel) subject to removal, an unbalance vector representing an amount and an azimuth direction of unbalance of a rotary fluid element is measured, and the unbalance vector is divided into divided vectors at a pair of cut-remove portions disposed on either side of the azimuth direction of the unbalance vector. If an unbalance amount corresponding to each divided vector is greater than the maximum amount that can be cut and removed for the corresponding cut-remove portion, the divided vector is divided again into divided vectors at a pair of cut-remove portions disposed on either side of the azimuth direction, and the re-division is repeated until an unbalance mount corresponding to each divided vector reaches or falls below the maximum amount that can be cut and removed for the corresponding cut-remove portion, before cutting and removing the resulting cut-remove portions.
In this processing method for correcting unbalance described in Patent Document 1, on the basis of a measured unbalance vector, processing is performed on a single location radially outside a cut-remove portion of a rotary member corresponding to the unbalance vector, or at each location (multiple locations in total) radially outside each of a plurality of different cut-remove portions of the rotary member corresponding to divided vectors.
Herein, an amount of unbalance is represented by a product of mass and length, and thus a correction amount of unbalance can be increased with a greater length. Accordingly, unbalance is normally corrected by cutting and removing a radially-outside rim portion of a rotary fluid element.